The XMM-Newton Serendipitous Source Catalogue:
2XMMi-DR3

User Guide to the Catalogue

This User Guide refers directly to the full FITS and plain-text formats of
the catalogue. Users interested in the details of the data processing can
refer directly to section 2 and using the link from there to the 2XMM User
Guide. Users interested in the main properties of the catalogue will find the
summary and sections 1 & 5 of most immediate interest.

Summary

2XMMi-DR3 is the latest increment of the second catalogue of
serendipitous X-ray sources from the European Space Agency's (ESA)
XMM-Newton observatory, and has been created by the XMM-Newton Survey
Science Centre (SSC) on behalf of ESA. The catalogue has 836 more
observations and about 64000 (22%) more detections than the preceding
2XMMi catalogue, which was made public in August 2008. The processing used
to generate the 2XMMi-DR3 catalogue is essentially the same as used for
2XMM and 2XMMi and is based on the pipeline developed for the
re-processing of all XMM observations conducted in 2006/7.

The catalogue contains source detections drawn from a total of
4953 XMM-Newton EPIC
observations made between 2000 February 3 and 2009 October 08;
all datasets included were publicly available by 2009 October 31 but
not all public observations are included in this catalogue. The total area
of the catalogue fields is ~ 814 deg2, but taking
account of the substantial overlaps between observations, the net sky area
covered independently is ~ 504 deg2.

The catalogue contains 353191 X-ray source detections above the
processing likelihood threshold of 6. The 353191 X-ray source detections
relate to 262902 unique X-ray sources, that is, a significant fraction of
sources (41979) have more than one detection in the catalogue.

The catalogue distinguishes between extended emission and point-like
detections. Parameters of detections of extended sources are only reliable
up to the maximum extent measure of 80 arcseconds. There are 30470
detections of extended emission, of which 5770 are 'clean' (i.e., have not
received a manual flag).

Due to intrinsic features of the instrumentation as well as some
shortcomings of the source detection process some detections are considered
to be spurious or their parameters are considered to be unreliable. It is
recommended to use either a detection flag or an observation flag as a
filter to obtain what can be considered a 'clean' sample. There are 284270
out of 353191 detections that are considered to be clean (i.e., summary
flag < 3), and 2318 out of 4953 fields are considered to have
no or at most a couple of spurious detections in them (observation
class < 2).

For 56017 detections spectra and time series were automatically
extracted during processing, and a χ2-variability test was
applied to the time series. 3177 detections in the catalogue are considered
variable at a probability of 10-5 or less based on the
null-hypothesis that the source is constant.

The median flux (in the total photon-energy band
0.2 - 12 keV) of the catalogue detections is
~ 2.5 × 10-14 erg/cm2/s; in
the soft energy band (0.2 - 2 keV) the median flux is
~ 5.6 × 10-15, and in the hard band
(2 - 12 keV) it is
~ 1.4 × 10-14. About 20% have fluxes below
1 × 10-14 erg/cm2/s. The
positional accuracy of the catalogue point source detections is
generally < 5 arcseconds (99% confidence radius). The flux values
from the three EPIC cameras are, overall, in agreement to ~ 10% for
most energy bands.

Though the 2XMMi-DR3 catalogue is a catalogue of serendipitous sources,
the observations from which it has been compiled are pointed observations
with one or more targets. An analysis to identify the target of each
observation and to classify the contents of the field with regard to its
serendipity has been carried out. In about 64% of the cases, one or
(occasionally) more detections could be directly identified with the
target(s) of the observations.

1. Introduction

Pointed observations with the XMM-Newton Observatory detect significant
numbers of previously unknown 'serendipitous' X-ray sources in addition to
the proposed target. Combining the data from many observations thus yields
a serendipitous source catalogue which, by virtue of the large field of
view of XMM-Newton and its high sensitivity, represents a significant
resource. The serendipitous source catalogue enhances our knowledge of the
X-ray sky and has the potential for advancing our understanding of the
nature of various Galactic and extragalactic source populations.

The 2XMMi-DR3 catalogue is the fifth publicly released XMM X-ray source
catalogue produced by the XMM Survey Science Centre (SSC) consortium. It
follows the 1XMM (released in April 2003), 2XMMp (July 2006), 2XMM (August
2007) and 2XMMi (August 2008) catalogues: 2XMMp was a preliminary version
of 2XMM. 2XMMi and 2XMMi-DR3 are incremental versions of the 2XMM
catalogue.

With this increment catalogue, for the first time, as part of the
catalogue naming convention we introduce the concept of a data release (DR)
as a means of distinguishing between increments - see
version definitions. In this
scheme, 2XMM is considered as DR1, 2XMMi as DR2 and the present catalogue
as DR3.

The 2XMMi-DR3 catalogue is about 22% larger than the 2XMMi catalogue,
which it supersedes, due to the ~1.5-year longer baseline of observations
included. As such, it is the largest X-ray source catalogue ever produced,
containing more than twice as many discrete sources as either the ROSAT
survey or pointed catalogues. 2XMMi-DR3 complements deeper Chandra and
XMM-Newton small area surveys, probing a large sky area at the flux limit
where the bulk of the objects that contribute to the X-ray background lie.
The 2XMMi-DR3 catalogue provides a rich resource for generating large,
well-defined samples for specific studies, utilizing the fact that X-ray
selection is a highly efficient (arguably the most efficient) way of
selecting certain types of object, notably active galaxies (AGN), clusters
of galaxies, interacting compact binaries and active stellar coronae. The
large sky area covered by the serendipitous survey, or equivalently the
large size of the catalogue, also means that 2XMMi-DR3 is a superb resource
for exploring the variety of the X-ray source population and identifying
rare source types.

The production of the 2XMMi-DR3 catalogue has been undertaken by the
XMM-Newton SSC consortium in fulfilment of one of its major
responsibilities within the XMM-Newton project. The catalogue production
process has been designed to exploit fully the capabilities of the
XMM-Newton EPIC cameras and to ensure the integrity and quality of the
resultant catalogue through rigorous screening of the data.

The earlier 2XMM catalogue was made from a subset of public observations
emerging from a re-processing (in 2006/7) of all XMM observations made
prior to that point. The first increment, 2XMMi, included a further 626
observations. These came from a) observations from the re-processing that
had been proprietary at the time of the 2XMM release but which subsequently
became public before 01 May 2008 and b) 90 observations that had been
processed as part of the routine, day-to-day XMM data processing performed
by the SSC, after the 2006/7 re-processing and which were also public at 01
May 2008. The processing pipeline used for the latter was essentially
identical to that used for the re-processing.

The new 2XMMi-DR3 catalogue augments the 2XMMi data with a further 836
observations, 89 of which come from the 2006/7 re-processing and were
public by 31 October 2009. The bulk of the extra data are from suitable
observations from the more recent routine day-to-day pipeline processing
operations which were also public by 31 October 2009. It should be noted
that 14 observations (675 detections) in the 2XMMi-DR3 catalogue come from
day-to-day processings performed since 15 April 2009 using a pipeline in
which newer energy conversion factors (ECFs) are used in converting count
rates to fluxes than were used for 2XMM/2XMMi (see Sec 6.2.1 and Sec 6.2.2 ). The largest change in ECF is
approximately 8% and affects the MOS1 and MOS2 band 1 fluxes when observing
with the THICK filter. Otherwise the changes in the ECFs are < 5%.

Users of the 2XMMi-DR3 catalogue should note that every detection in
2XMM and 2XMMi appears in 2XMMi-DR3 with the same detection identifier,
DETID. New detections have DETID values > 289084. In general the
2XMM and 2XMMi unique source identifiers, SRCID, have also been preserved
but in a small number of cases, detections from 2XMM or 2XMMi sources were
regrouped and, in rare cases (essentially restricted to complex regions),
sources from 2XMM or 2XMMi no longer appear in 2XMMi-DR3, being replaced by
new sources comprised of different arrangements of detections (see Sec 3.2). Since detections can occasionally be
allocated to a different source in the 2XMMi-DR3 catalogue, earlier SRCID
values can disappear but they are not reallocated so that gaps in the SRCID
sequence can occur. The 2XMMi-DR3 catalogue provides information that
indicates where changes have occurred.

2. User Guide for 2XMM

The extensive User Guide (UG)
for the 2XMM catalogue describes all the details of the data processing
and compilation of the catalogue. As with 2XMMi, the 2XMMi-DR3 catalogue
processing is practically unchanged. In the following section the differences or updates for the
2XMMi-DR3 catalogue with respect to 2XMMi are described. For convenience,
Table 1, which gives the energy band
definition, is repeated here.

3. 2XMMi-DR3 -- differences and additions with
respect to the 2XMMi catalogue

3.1 Data selection

The selection of XMM-Newton observations for inclusion in the 2XMMi-DR3
catalogue follows the same guidelines as for the 2XMM and 2XMMi catalogues
but with a new cut-off for the public release date: All observations that
have a public release
date prior to 2009 October 31 were eligible for inclusion. Table 2.1 gives the list of the final 4953
observations (3491 from 2XMM, 626 from 2XMMi and 836 new) which are
included in the 2XMMi-DR3 catalogue.

3.2 Unique celestial sources

The details of the procedure used for matching detections in to unique
sources on the sky is described in the 2XMM UG,
Sec. 3.2.3 a). For 2XMMi, essentially the same process was
adopted, albeit with a small correction but it was necessary to consider
the impact of merging the new detections available for 2XMMi with the ones
already in 2XMM. This was explained in the 2XMMi UG,
Sec. 3.2.1 a). As noted above, occasionally this process can
result in a
change of the unique source to which a previous detection is allocated. For
2XMMi-DR3 we have adopted essentially the same mechanism for merging
detections, allowing the detections to be grouped from scratch. However, we
describe below some alterations to the way in which such changes are
flagged in the 2XMMi-DR3 catalogue.

3.2.1 Re-matching and representation of changes

The process of finding the set of detections which appear to come from
the same source and thus have a single SRCID number is simple and
unambiguous in most of the sky. However, in a few areas, for example in
ridges of extended emission or in shells around SNRs, the
detection-matching process produces results which are occasionally unstable
in the sense that minor changes to the parameters of the algorithm produce
slightly different matches.

In addition, the inclusion of new detections in the catalogue can lead
to cases where previous sources can be coalesced or a single course can
fragment. In either case, or in cases where a new detection simply joins an
existing unique source, the parameters of the unique source can be
modified.

In 2XMMi, two flags were introduced, SC_CHFLAG1 and
SC_CHFLAG2, to
signify the detailed nature of such changes. In 2XMMi-DR3 this useful but
somewhat complicated flagging scheme is replaced by a simpler concept. In
2XMMi-DR3, we utilize the following two flags,

i)

SC_DR_FIRST signifies the data
release of the catalogue in the 2XMM series in which the source with
this SRCID first appeared (DR1 represents 2XMM, DR2 represents 2XMMi
and DR3 represents 2XMMi-DR3). Note that where
SC_DR_FIRST = DR1, the IAU name retains the 2XMM prefix
(Sec 3.2.2). Where
SC_DR_FIRST = DR2 the IAU name prefix is 2XMMi and it is
also 2XMMi when SC_DR_FIRST = DR3.

ii)

SC_DR_LAST signifies the data
release of the catalogue in the 2XMM series in which the source with
this SRCID was last updated in any way.

In 2XMMi-DR3 we also introduce another new flag which indicates where
there is uncertainty about which unique source a detection is assigned
to. The CONFUSED flag
is set true for a unique source if any detections that comprise it overlap
with another unique source. This is taken to be the case if the 3 sigma
positional error (3 * POSERR)
of the detection overlaps the corresponding 3 sigma positional error of
any other unique source (which is located within 7 arc-seconds of it).

Note that the only changes in the catalogue parameters refer to the
unique source identification (SRCID), source (SC_*) parameters and IAUNAME. All parameters referring to an
observation or a detection remain unchanged.

A consequence of the fact that detections can be re-grouped during the
matching procedure is that 170 sources in 2XMMi do not appear in 2XMMi-DR3
and 438 sources from 2XMM are absent from 2XMMi-DR3 but the detections are
still present with different SRCID values. The SRCID_2XMMi parameter can be used to
find the original 2XMMi source ID for detections from the 170 sources
from 2XMMi that are not in 2XMMi-DR3.

3.2.2 IAU identification

An IAU identification, IAUNAME, has been assigned to each unique
source (SRCID) based upon the
IAU registered classifications 2XMM and 2XMMi: a source that is included in
the 2XMM catalogue has kept its 2XMM IAU identification; a source that
appeared for the first time in 2XMMi retains its 2XMMi IAU identification;
all new sources in 2XMMi-DR3 are also assigned an IAU name with a 2XMMi
prefix.

The form of the IAU names is "2XMM Jhhmmss.sSddmmss" or
"2XMMi Jhhmmss.sSddmmss" where hhmmss.s is taken from the averaged and
eposcorr corrected right ascension coordinate given in the column
SC_RA and Sddmmss is the
averaged and eposcorr corrected declination taken from the column
SC_DEC of the respective
catalogue. Note that the averaged coordinates may have changed with respect
to 2XMM but the IAU name with the 2XMM prefix will be the same as in the
2XMM catalogue. The situation is similar for sources in the 2XMMi catalogue
where the 2XMMi prefixed IAU name is maintained.

The correct nomenclature for references to detections in the catalogue
is the IAUNAME followed by a
colon and the detection identification number DETID (with six digits), that is:
"2XMM Jhhmmss.sSddmmss:detid" and
"2XMMi Jhhmmss.sSddmmss:detid".

3.3 Updated summary html pages

Summary html pages are provided for each detection and are all newly
generated, regardless of whether the detection is new or not or whether
anything has changed with regard to a unique source that the detection
belongs to. Where the unique source has changed, its new parameters are
updated in the html page. Links to the html summary pages of the other
constituent detections of the unique source are embedded in the page. They
can be accessed through LEDAS. The slimline catalogue lists a column with
the LEDAS URL which can be activated from within applications such as
topcat.

3.4 Updated visual screening

The distribution of the six observation classes has slightly changed
with respect to 2XMM and 2XMMi due to the continued trend of increasing
occurences of 'noisy' CCDs (mainly CCD 4 of MOS1 and CCD 5 of MOS 2) in the
more recent observations. Table 4
lists the observation class, the fractional area of exclusion with respect
to the total detection area, and the percentage of observations affected
for the 2XMMi-DR3, 2XMMi and 2XMM catalogues as well as for the new
observations.

Table 4: Distribution of observation class for
the 836 new observations and for the overall observation sets used in
the 2XMMi-DR3, 2XMMi and 2XMM catalogues

Obs class

'bad' area fraction

New
observations

2XMMi-DR3

2XMMi

2XMM

0

0% area

26%

35%

37%

38%

1

0% < area < 0.1%

10%

12%

12%

12%

2

0.1% <= area < 1%

12%

10%

9%

10%

3

1% <= area < 10%

35%

28%

26%

25%

4

10% <= area < 100%

15%

12%

11%

10%

5

100%

3%

4%

5%

5%

Total number of
observations

836

4953

4117

3491

3.5 Updated target classification

An ascii list showing the target, and, where identified, its 2XMMi-DR3
counterpart and classification, for each observation in 2XMMi-DR3, will
be available shortly. A corresponding fits file will also be made
available. A more detailed description of the process applied to 2XMM and
2XMMi is given in SSC-LUX-TN-0065.ps. A new update, reflecting
changes in the target identification procedure applied to 2XMMi-DR3,
will accompany the release of the target list.

4. Catalogue content and organisation

This section summarises the organization of the catalogue and gives
details of all the columns. Known problems with parameters presented in the
catalogue or with products associated with it are listed in Sec. 6.

There are 299 columns in the catalogue; they are grouped together and
explained in the links below.

For each observation there are up to three cameras with one or more
exposures which were merged when the filter and submodes were the same
(2XMM UG,
Sec. 2.2). The data in each exposure are accumulated in several
distinct energy bands (Table 1). Camera-level
measurements can further be combined into observation-level parameters.
Consequently, the source parameters can refer to some or all of these
levels: on the
observation level there are the final mean parameters of the source (prefix
'EP'); on the camera level the data for each of the three cameras (where
available) are given (prefix 'PN', 'M1', or 'M2'), and on the energy band
level the energy-dependent details of the source parameters are given
(indicated by a 'b' in the column name where b = 1,2,3,4,5,8,9). Finally,
on a meta-level, some parameters of sources that were detected more than
once (prefix 'SC') were combined, see 2XMM UG, Sec. 3.2.4.

The column name is given in capital letters, the FITS data format in
brackets and the unit in square brackets. If the column originates from a
SAS task, the name of
the task is given to the right hand side and a link is set to the
SAS
6.9 package documentation with which the bulk of the data
in the 2XMMi-DR3 catalogue was processed
(see 2XMM UG,
App. A.3 for more details). Note that documentation for the
latest public version of the SAS can be found
here. A description
of the column and possible cross-references follow.

Entries with NULL are given when no detection was made
with the respective camera, that is, ca_MASKFRAC < 0.15 or
NULL (i.e., a camera was not used in an observation).

Every detection in 2XMM and 2XMMi appears in 2XMMi-DR3 with the same
detection identifier, DETID.
New detections have DETID values of 289 084 or above. In general the 2XMM
and 2XMMi unique source identifiers, SRCID, have also been preserved but there
are a few cases in which this was not possible, see Sec. 3.2, but note the SRCID identifiers are not
re-assigned so they are simply dropped if the source no longer exists.

Details of the columns:

This includes the basic static identifiers, IAU name and
cross-reference to the 2XMMi source ID where relevant. 5 columns
that appeared in 2XMMi relating sources there to counterparts in the
1XMM and 2XMMp catalogues were considered superfluous and are removed
in 2XMMi-DR3

This part lists the flags to qualify the detections. The summary
flag, which gives an overall assessment for the detection, is
followed by particular flags for each camera. A flag each is given if
there exists at least one time series or one spectrum for this
source.

This part lists the source parameters for the unique sources
across all observations (using the prefix 'SC'); these are
coordinates, fluxes, hardness ratios, likelihoods, extent information
and a variability and a summary flag. The number of detections is
given also. In addition, flags are provided to indicate where the
constitution/parameters of unique sources has changed between
catalogues and where confusion of sources may be present. In
2XMMi-DR3 four new columns are
introduced in this section and the definition of another is
modified, while two columns from 2XMMi are dropped,
being replaced by the new ones.

Columns in the slimline catalogue:

Table 6 lists the 38 columns in the
2XMMi-DR3 'slimline' version of the catalogue, all of which are explained
in Part 1 or Part 7
of the 2XMMi-DR3 column description, except the LEDAS_URL column which is
described at the end of the table.

5.1 Overview

The catalogue contains source detections drawn from 4953 XMM-Newton EPIC
observations made between 2000 February 3 and 2009 October 8 and
which were publicly available by 2009 October 31. Net exposure times
in these observations range from < 1000 up to
~ 130000 seconds (that is, a full orbit of the satellite).
Figure 5.1 shows the distribution of
fields with net exposure time, Fig. 5.2
shows the distribution of fields on the sky.

The total sky area of the catalogue observations with effective
exposure > 1ksec is ~ 814 deg2 which translates to
~ 504 deg2 when corrected
for field overlaps. Figure 5.3 shows the sky area as a function of net
exposure time (based on vignetted exposure maps, cf. 2XMM UG,
Sec. 3.1.2 a)).

The catalogue contains 353191 X-ray detections with total-band
(0.2 -12 keV) likelihood values ≥ 6. Of these 262902
are unique X-ray sources (Sec. 3.2), that
is, 41979 X-ray sources were observed more than once and up to 38 times in
total. Of the 353191 X-ray detections 30470 are classified as
extended with 5770 of these being in regions considered to be 'clean'.

As part of extensive quality evaluation for the catalogue, each field
has been visually screened. Regions where there were obvious deficiencies
with the automatic source detection process were identified and
all detections within those regions were flagged (cf.
2XMM UG,
Sec. 3.2.6). Such flagged detections include spurious detections
(many of which are classified as extended) as well as detections where the
source parameters may be unreliable. It is recommended to use either a
detection flag (SUM_FLAG,
EP_FLAG or SC_SUM_FLAG) or an observation flag
(OBS_CLASS) as a filter
to obtain what can be considered a 'clean' sample. There are 246666 out of
353191 detections (70%) that have not received any flag designating a
possible
spurious detection or affected parameters, while 284270
out of 353191 detections (80%) can be considered to be 'clean', i.e., are
unlikely to be spurious due to insufficient background determination in the
source detection process (summary flag < 3). On the other
hand, 2789 out of 4953 fields are considered to have no or at most a couple
of spurious detections in them (observation class < 3). Note
that no attempt is made to flag spurious detections arising from
statistical fluctuations in the background though a preliminary analysis
of the false detection rate has been made (see 2XMMi UG, Sec. 5.2 for
a discussion of this).

Figure 5.4 presents, for each
of the three cameras, the distributions of flux for energy bands 1 to 5
and also for the combined (EPIC) data. These give an indication of the
limiting flux available in the catalogues for each of the bands.

As part of the procedure to verify the integrity of the new catalogue,
a number of comparisons of the 2XMMi-DR3 catalogue were made against
the predecessor 2XMMi catalogue. No significant issues were
identified. As an example, figure
5.5 compares the normalised distribution of the EPIC
fluxes from the incremental detections in 2XMMi-DR3 against that of
all the detections from 2XMMi. Plots are shown for energy bands 1 to 5.
The 2XMMi-DR3 fluxes are consistent with those from 2XMMi.

5.2 False detection rates

Analysis of the false detection rates in the 2XMM and 2XMMi catalogues has
been described in the 2XMMi UG, Sec. 5.2 and
also applies to 2XMMi-DR3.

6. Known problems and other issues

6.1 Problem cases

6.1.1 Incorrect variability measurement

A few cases have been noted where the detection shows a variability that
is due to incorrect handling of the data. Two reasons have been tentatively
identified:

Attitude GTIs are not included in the filtering criteria for
source product extraction. Occasionally a source was significantly
displaced with respect to the aperture as defined by the detection image
(in extreme cases, off the detector). This will affect the calculation
of count rates of the spectra and the variability measurements for the
time-series.

Occasionally the light curve exposure correction fails (i.e., no
time-series are produced) or inadequately corrected for strong
background variations across CCDs (which can cause spurious variability
detections). The latter cases are confined to very bright extended
sources and are mostly associated with spurious detections.

6.1.2 Dark columns in PN images are not represented
in the exposure maps

The presence of a broad dark column in some of the PN images (and which
is not represented in the exposure maps) is related to the onboard MIP
rejection and to bad pixels, see the Appendix of CAL-TN-0067-0-0.pdf.
As a consequence, the parameters of sources near these columns (with
distance < 60 srcseconds) are underestimated.

6.1.3 PN low energy noise can cause spurious
detections

Most of the PN low energy noise is suppressed by the use of
PATTERN 0 events. However, in some cases bright columns or clumps of
pixels appear in the images and may cause spurious detections. In most
cases detections on bright columns are automatically and manually flagged
(2XMM UG,
Table 3.3a). As the problem has become more significant in recent
years, manual flagging for new detections in 2XMMi-DR3 has also attempted
to flag detections of bright clumps (which were hitherto not flagged at
all). However, this process is necessarily subjective and uncertain. In
most cases these sources only appear in band 1 where they could, for
example, be misinterpreted as super-soft sources. As such, users are
warned to treat such detections with caution, whether flagged or not.

6.1.4 Spurious sources arising from MOS low energy
noise

In recent years, an increasing number of observations have shown clear
evidence of low energy noise affecting specific CCDs in the MOS cameras.
Generally but not exclusively, it is CCD4 or CCD5 in MOS1 and CCD2 and CCD5
in MOS2 that are affected and the effect is essentially confined to
energies below 1keV (bands 1 and 2). Affected CCDs often stand out in the
MOS images as having notably higher count levels compared to the adjacent
CCDs. Of itself, this increased noise primarily leads to reduced
sensitivity in the relevant CCD sky area.

However, a further significant impact arises in source detection because
the computation of the background map (see 2XMM UG, Sec. 3.1.2d) does
not adequately cope with the step transition in the brightness level
between the noisy CCD and adjacent CCDs. The result can be an over- or
under- representation of the background map in the vicinity of CCD boundary
and this can then lead to the detection of spurious (often extended)
sources near the edges of the noisy CCD where it borders another CCD. These
sources generally recieve a manual flag from the visual screening process
(see 2XMM UG,
Sec. 3.2.6) but users should be aware of the issue.

6.2 Other issues

6.2.1 New calibrations and improved fluxes

Since early 2008, improvements in the calibration of the MOS and PN
have occurred which lead to slight changes in the ECFs, particular in the
soft energy bands. These, however, have not been applied in the pipeline
processing of most of the observations used in making 2XMMi-DR3 (but see
Sec. 6.2.2).
Therefore, Table 8 gives correction factors
to be applied to the ECFs and fluxes that were used in the catalogue (see
2XMM UG, Table 3.2
for the original ECFs) in the sense

Table 8: Correction factors to the ECFs and
fluxes used in 2XMM and 2XMMi processing

Camera

Band

Open

Thin

Medium

Thick

PN

1

1.02176

1.01139

1.00767

0.997455

2

1.02128

1.02017

1.02007

1.01950

3

0.999321

0.999288

0.999274

0.998995

4

1.01190

1.01152

1.01136

1.01107

5

1.00063

1.00000

1.00000

1.00064

9

1.01128

1.00974

1.00996

1.00902

MOS-1

1

0.981613

0.956452

0.945457

0.925115

2

0.961381

0.961301

0.960208

0.960476

3

0.988680

0.988948

0.988765

0.989250

4

1.00000

1.00074

1.00000

1.00000

5

1.00194

1.00171

1.00170

1.00173

9

0.977969

0.978943

0.979105

0.98017

MOS-2

1

0.989302

0.959068

0.946630

0.922199

2

0.961461

0.960747

0.960899

0.959776

3

0.991415

0.991824

0.991676

0.992057

4

1.00073

1.00000

1.00075

1.00000

5

1.00300

1.00300

1.00301

1.00305

9

0.979524

0.980446

0.980451

0.981477

Note that newer canned
redistribution matrices are available which, in particular, take account
of the
spatial affects in the MOS near the boresight. These will have a further
impact on the ECFs but ECFs including these effects have not been
generated for use in the pipeline processing of observations used in any
of the current XMM catalogues.

6.2.2 Observations in 2XMMi-DR3 using updated
ECFs

Fourteen observations in 2XMMi-DR3 are publicly available observations
processed by a pipeline running since 15 April 2009 that accessed newer ECF
values than used for 2XMM and 2XMMi. Table 9 identifies these 14
observations. For these cases, the correction factors shown in Table 8 do not need to be applied.

6.2.3 Mismatch between catalogue and an archived product set

One observation, OBS_ID = 0400010201 from revolution 1341, has been
reprocessed again since the reprocessing in 2007 and the official, formal
pipeline products from the original processing have been overwritten and
are irrecoverable. These new products have also been archived in the XSA,
replacing the originals. The new processing yielded 136 detections, 6
fewer than the original - this is essentially a consequence of
marginally significant detections that can change due to the pixel-level
spatial randomization of events during processing. To maintain consistency
with 2XMMi, however, the original detection information has been used in
2XMMi-DR3. This means that the number of detections and the parameters of
the detections in the 2XMMi-DR3 catalogue, for this one observation, are
not consistent with the observation summary source list product currently
held in the XSA.

6.2.4 High proper motion objects

No epoch information is used when matching detections to construct
unique
sources. As a consequence, detections of high proper motion stars from
multiple observations spanning a significant period of time may not have
been matched into a single unique source. A good example is 61Cyg whose
proper motion between observations from early XMM-Newton revolutions used
in 2XMM and 2XMMi and observations from more recent revolutions available
in 2XMMi-DR3 is appreciable. The source is mapped to several distinct
sources due to its movement (e.g. 2XMM J210654.9+384505 and 2XMMi
J210656.8+384524). However, the less conservative criteria for recognizing
potential confusion result in it being flagged as CONFUSED (see Sec.
3.2.1), the confusion
arising from positional overlaps with other detections of itself.